Copy paste Playonline Folder from old to new pc.
( Also , copy USER folder into new pc from old , this hold game setting , and macros if you need )
(ex: C:\Program Files (x86)\PlayOnline\SquareEnix\FINAL FANTASY XI\USER)

Run POL >

Pol will check file and update .

log into game once ( might load macros if saved on server on character page )

Yeah, definitely use the new installer, and you should probably just format that old drive.

Generally if you have to ask when it comes to the registry you shouldn't be doing it, BUT there are guides out there, even premade batch files that will reregister the .dlls for you. Still just recommend doing a fresh install, now Windower you can just copy the directory and make a new shortcut.